Toto Aquis buttons
I installed two Toto Aquia toilets. One button set work fine the other one had a slight problem with the bigger button(used for larger flush), rubbing a little a bit against the smaller button as it get pushed. I swappedthe cover on the good one on with the cover on the bad one and still the bad cover had the problem. It is not the toilet valve problem but the plastic buttons and the button assembly, which is also made of plastic. All it takes, is little bit of off alignment and the two buttons will develop a little fiction, or rub against each other or against the button assembly. I pushed the two buttons up and down in the assembly for a while after removing it from the cover to develop some wear on it. Then I sprayed a little W2-40 oil on the buttons and the between the button s and the assembly to give it a little more freedom of movement. That seems to have helped some. You might try that. Short of that, just get another whole assembly unit.